A concensus sequence of the potential LDL receptor binding domain has been determined based on computer evaluation of the amino acid sequence of apoB-100, and an analysis of monoclonal antibodies which block LDL-LDL receptor interaction. Synthetic peptides based on the sequence of the potential LDL receptor binding domain have been prepared, and have been shown to increase the binding and degradation of apoB-48 lipoproteins incubated with normal human fibroblasts. Additional synthetic peptides are currently being evaluated in order to further define the structure-function requirements for binding of LDL to the LDL receptor. Human apoB-100 and apoA-I have been shown to be acylated with fatty acid in HepG-2 media. Quantitation of acyl groups on plasma apoB-100 and apoA-I by gas chromatography revealed no fatty acids establishing that circulating plasma apoA-I and apoB- 100 are not acylated. Acylation may therefore play an important role in intracellular transport of plasma apolipoproteins. Analysis of apoB isoproteins secreted from the human intestine revealed that apoB-100 is the primary apoB isoprotein secreted in children ages 1 to 5. Further studies are underway to evaluate the apoB isoproteins secreted in adult intestine.